An X-ray image detector is an apparatus that converts an X-ray that has transmitted through a subject to visible light and is used for medical diagnosis apparatuses, nondestructive inspectors, and so on as an X-ray image intensifier or the like.
Such an X-ray image detector is configured such that an input part that converts an X-ray to photoelectrons and an output part that converts the photoelectrons to visible light are respectively provided on both end portions of a vacuum envelope made of, for example, metal or glass. A focusing electrode and an anode to accelerate and focus the photoelectrons emitted from the input part and directed to the output part are interposed between the input part and the output part. An X-ray image incident on the X-ray image detector is outputted as a visible light image after passing through the input part and the output part. Then, the visible light image outputted from the X-ray image detector is photographed by a CCD camera or the like, so that a subject image is displayed on a monitor television or the like.
The input part of the X-ray image detector is composed of an input substrate having a recessed surface in a shape of, for example, a dome, an X-ray light emitting phosphor film such as a CsI (cesium iodide) film formed by a deposition method on the recessed surface of the input substrate, a transparent conductive film formed on the X-ray light emitting phosphor film, and a photoelectric surface formed on the transparent conductive film. An aggregation of columnar crystals of CsI growing substantially vertically to the input substrate is used as the CsI film constituting the X-ray light emitting phosphor film. The columnar crystals of CsI are separated by minute gaps from one another to increase sharpness of separation between channels, which makes it possible to obtain a high resolution characteristic.
The CsI film mainly formed of the above-mentioned columnar crystals, besides being formed such that the columnar crystals are separated by the minute gaps from one another, has recessions and protrusions formed by tip portions of the columnar crystals. Since the formation of the transparent conductive film and the photoelectric surface on such a CsI film lowers or prevents electrical conduction in the direction of these surfaces, it is necessary to make the surface of the CsI film mainly formed of the columnar crystals continuous and flat. As for the continuous formation of the CsI film, a method of forming a continuous film of CsI on a CsI film mainly formed of columnar crystals in a highly vacuum atmosphere is known as described in, for example, Japanese Patent Laid-open Application No. Hei 2-170331.
In the above-mentioned method of forming the continuous film of CsI, increase in film-growth time and so on are caused and in addition, a sufficient effect of flattening the CsI film cannot be obtained. Therefore, such a method is used in which a plurality of metal balls are rolled on a CsI film mainly formed of columnar crystals to make a surface portion of the CsI film continuous and flat (see Japanese Patent Laid-open Application No. Hei 3-22325 and Japanese Patent Laid-open Application No. Hei 3-280325). This method is a method of plastically deforming top portions of the columnar crystals through the utilization of the weight of the metal balls to thereby make the surface portion of the CsI film continuous and flat.
The above-mentioned flattening method using the balls, however, requires uniform application of the weight of the balls on the entire CsI film, so that the process time required for flattening the CsI film becomes long. Further, due to the irregular movement of the balls, it is difficult to control planarity of the CsI film. Imparting regularity to the movement of the balls in order to control planarity will give rise to such a problem that the regular movement hinders planarity.
Further, Japanese Patent Laid-open Application No. 2001-93415 describes a method of pressurizing a CsI film mainly formed of columnar crystals in a heated state by a roller moving along a recessed surface (for example, a spherical surface) of an input substrate to thereby make a surface portion of the CsI film continuous and flat. This method can enhance controllability over planarity of the CsI film, but on the other hand, limits the shape of the recessed surface of the input substrate due to a limited movement route of the roller used for flattening.
It is an object of the present invention to provide a method and a device for producing an X-ray image detector capable of efficiently and uniformly flattening an X-ray light emitting phosphor film. It is another object to provide an X-ray image detector to which such a flattening method is applied to enable improved resolution and display sharpness of an X-ray image.